Vertebral body spacer

ABSTRACT

A vertebral body spacer of the present invention is used by being inserted between a vertebral body and a vertebral body (intervertebral space). The vertebral body spacer has a block body constituted of titanium or a titanium alloy as a main component thereof, and provided with a pair of contact surfaces to be made contact with the vertebral body and the vertebral body. The block body includes a frame-shaped dense part and a porous part provided inside the dense part, and a porosity of at least a surface of the porous part is larger than a porosity of the dense part. According to the present invention, it is possible to maintain an appropriate size between the vertebral bodies (intervertebral space).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 13/884,424 filed May 9, 2013 which claims the right of priorityunder 35 U.S.C. §119 based on Japanese Patent Application No.2010-252228 filed Nov. 10, 2010.

This application is related to PCT applications, entitled, “VERTEBRALBODY SPACER” in the names of Toshio Matsumoto, Yuzo Daigo, ShinichiOhmori and Komei Kato, Nos. PCT/JP2011/075841 (U.S. Pat. No. 9,549,821issued Jan. 24, 2017) and PCT/JP2011/075836 (U.S. Ser. No. 13/884,439filed May 9, 2013) both filed Nov. 9, 2011, which the US counterparts ofthe PCT applications are assigned to the assignee of the instantapplication and which the US counterparts of PCT applications are alsoincorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a vertebral body spacer.

RELATED ART

Spinal canal stenosis is caused by degeneration of an intervertebraldisk interposed between adjacent vertebral bodies (intervertebralspace), degenerative facet joint disease, secondary deformation of avertebral body, spinal deformation, or the like, and results in caudaequina/nerve root disorders.

One approach for treating such spinal canal stenosis includes interbodyfusion in which a degenerated intervertebral disk is removed frombetween the adjacent vertebral bodies, and then used is an vertebralbody fusion surgery of fusing the vertebral bodies by implanting anautologous bone into an intervertebral space in which the intervertebraldisk has been removed.

However, in a case where only bone grafting into the intervertebralspace is carried out, there is a possibility that unstable fusingbetween the vertebral bodies is caused by resorption of a grafted boneuntil bone fusion is achieved. Further, an amount capable of harvestingan autologous bone is limited, so that there is a possibility that abone to be grafted is not acquired in a sufficient amount.

Therefore, used is a method of fusing the vertebral bodies stably byinserting a vertebral body spacer by itself as a substitute material ofan autologous bone or the vertebral body spacer together with theautologous bone into the intervertebral space.

In this case, it is required that this vertebral body spacer supportsvertebral bodies stably and fuses with the vertebral bodies easily. Froma point of such a view, a constituent material and a shape of thevertebral body spacer have been studied, so that various kinds ofvertebral body spacers have been developed (for example, Patent Document1).

Such a vertebral body spacer, generally, is constituted from a blockbody having a uniform porosity. Such a porosity is set to fall withinthe range of about 30 to 60% for a purpose of achieving bone fusionbetween the vertebral body spacer and vertebral bodies making contactwith the vertebral body spacer promptly.

However, it is impossible for the vertebral body spacer having theporosity falling within such a range to withstand stress on thevertebral body spacer depending on a body type of a patient to which thespacer is to be applied and a position of an intervertebral space suchas lumbar vertebra and cervical vertebra. As a result, there is a fearthat the vertebral body spacer is broken by the stress.

Patent Document: JP 2002-95685 A

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a vertebral bodyspacer that is capable of maintaining an appropriate size betweenvertebral bodies (intervertebral space) and reliably preventing thevertebral body spacer from being broken irrespective of cases and aposition of the intervertebral space, and thereby capable of achievingbone fusion between the vertebral body spacer and vertebral bodiespromptly.

The object is achieved by the present inventions (1) to (8) describedbelow.

(1) A vertebral body spacer to be used by being inserted betweenvertebral bodies, comprising;

at least one block body constituted of titanium or a titanium alloy as amain component thereof, and the block body having a pair of contactsurfaces to be made contact with the vertebral bodies, and

wherein the block body includes a frame-shaped dense part and a porouspart provided inside the dense part, and a porosity of at least asurface of the porous part is larger than a porosity of the dense part.

This makes it possible to maintain a suitable size between the vertebralbodies (intervertebral space). Further, it is possible to reliablyprevent the block body from being broken irrespective of cases(patients) and a position of the intervertebral space, and therebycapable of achieving bone fusion between the block body and thevertebral bodies promptly.

(2) In the vertebral body spacer in above-mentioned item (1), the densepart and the porous part are integrally formed.

According to the vertebral body spacer mentioned above, in a state ofinserting the block body into the intervertebral space, it is possibleto reliably prevent stress from being applied to the dense part or theporous part unevenly when the stress is applied to the block body.

(3) In the vertebral body spacer in above-mentioned item (1), the porouspart has a plurality of corner portions, and the dense part is providedalong the plurality of corner portions of the porous part.

According to the vertebral body spacer mentioned above, the dense partis formed so as to define the whole shape of the block body.

(4) In the vertebral body spacer in above-mentioned item (1), the blockbody is constituted from a polyhedral body defined by a plurality ofsurfaces including the pair of contact surfaces, and each of theplurality of surfaces constitutes a flat surface.

This makes it possible to reliably make the porous part contact with thevertebral bodies. Therefore, it is possible to achieve the bone fusionbetween the porous part and the vertebral bodies promptly.

(5) In the vertebral body spacer in above-mentioned item (1), at leastone block body is constituted from a pair of block bodies.

This makes it possible to change a position of the pair of block bodies,namely to position the pair of block bodies in a state of spacing frontends and back ends of the pair of block bodies from each other and/orapproaching them to each other. Therefore, it is possible to provide anappropriate cure depending on cases by using such a vertebral bodyspacer.

(6) In the vertebral body spacer in above-mentioned item (1), a whole ofthe porous part is constituted from a porous body.

This makes it possible to achieve the bone fusion between the porouspart and the vertebral bodies promptly. Therefore, it is possible toreliably fuse the block body in the intervertebral space.

(7) In the vertebral body spacer in above-mentioned item (1), anosteoinductive factor is carried on the porous part.

This makes it possible to achieve the bone fusion between the porouspart and the vertebral bodies promptly.

(8) In the vertebral body spacer in above-mentioned item (1), the densepart includes a first frame portion to be made contact with one of thevertebral bodies, a second frame portion to be made contact with theother of the vertebral bodies and at least one connecting portionconnecting the first frame portion and the second frame portion to eachother, and wherein the connecting portion serves as a supporting post.

This makes it possible to improve strength of the dens part. Therefore,in a state of inserting the block body into the intervertebral space, itis possible to reliably suppress or prevent the dense part from beingbroken when the stress is applied to the block body.

According to the vertebral body spacer of the present invention, it iscapable of maintaining the appropriate size between the vertebral bodies(intervertebral space). Further, it is possible to reliably prevent thevertebral body spacer from being broken irrespective of the cases andthe position of the intervertebral space, and thereby capable ofachieving the bone fusion between the vertebral body spacer and thevertebral bodies promptly.

Further, by inserting the vertebral body spacer into the intervertebralspace, it is ensured to obtain a space for filling a filler into theintervertebral space. Therefore, by filling, for example, a grafted boneinto such a space, it is possible to achieve the bone fusion between thevertebral bodies through the vertebral body spacer and the grafted bonemore reliably and promptly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view (a), a front view (b) and a side view (c) whichshow a first embodiment of a block body constituting a vertebral bodyspacer of the present invention.

FIG. 2 is a view showing a used state of the first embodiment of thevertebral body spacer of the present invention.

FIG. 3 is a view showing a used state of the first embodiment of thevertebral body spacer of the present invention.

FIG. 4 is a plan view (a), a front view (b) and a side view (c) whichshow a second embodiment of a block body constituting a vertebral bodyspacer of the present invention.

FIG. 5 is a plan view (a), a front view (b) and a side view (c) whichshow a third embodiment of a block body constituting a vertebral bodyspacer of the present invention.

FIG. 6 is a plan view (a), a front view (b) and a side view (c) whichshow a fourth embodiment of a block body constituting a vertebral bodyspacer of the present invention.

FIG. 7 is a plan view (a), a front view (b) and a side view (c) whichshow a fifth embodiment of a block body constituting a vertebral bodyspacer of the present invention.

FIG. 8 is a view showing a used state of the fifth embodiment of thevertebral body spacer of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, description will be made on a vertebral body spaceaccording to the present invention in detail with reference to preferredembodiments shown accompanied drawings.

First Embodiment

First, description will be made on a first embodiment of the vertebralbody space according to the present invention.

FIG. 1 is a plan view (a), a front view (b) and a side view (c) whichshow the first embodiment of a block body constituting the vertebralbody spacer of the present invention. FIG. 2 and FIG. 3 are a viewshowing a used state of the first embodiment of the vertebral bodyspacer of the present invention, respectively.

In the following description, it is to be noted that a state ofinserting the vertebral body spacer between vertebral bodies of a case(patient) is defined as a basic state, thereby defining a positionthereof, unless it is explicitly stated otherwise.

Specifically, a ventral side of the patient (namely, a right side ineach of FIG. 1(a), FIG. 1(b) and FIG. 2(b), a near side in each sheet ofFIG. 1(c) and FIG. 2(a), and a lower side in FIG. 3) will be referred toas “front”, and a dorsal side of the patient (namely, a left side ineach of FIG. 1(a), FIG. 1(b) and FIG. 2(b), a back side in each sheet ofFIG. 1(c) and FIG. 2(a), and an upper side in FIG. 3) will be referredto as “back”. Further, a head side of the patient (namely, an upper sidein each of FIG. 1(b) and FIG. 2, a near side in each sheet of FIG. 1(a)and FIG. 3, and a left side in FIG. 1(c)) will be referred to as“upper”, and a leg side of the patient (namely, a lower side in each ofFIG. 1(b) and FIG. 2, a back side in each sheet of FIG. 1(a) and FIG. 3,and a right side in FIG. 1(c)) will be referred to as “lower”. It is tobe noted that a position of the vertebral body spacer in each of FIGS. 4to 8 is also defined as the same as those in FIGS. 1 to 3.

As shown in FIG. 2, a vertebral body spacer 1 is inserted between avertebral body 101 and a vertebral body 102 (hereinafter, referred to as“intervertebral space”) at the time of fusing the upper vertebral body101 and the lower vertebral body 102 after an intervertebral disk hasbeen removed. It is ensured to maintain (hold) an appropriate space(distance) between the vertebral body 101 and the vertebral body 102 ina state of inserting the vertebral body spacer 1 into the intervertebralspace (hereinafter, referred to as “inserted state”).

In the present embodiment, as shown in FIG. 2(a) and FIG. 3, thevertebral body spacer 1 (hereinafter, simply referred to as “spacer 1”)is constituted from a pair of elongated block bodies 2, 2. Each of theblock bodies 2, 2 is substantially identical to each other in a shape(constitution).

As described above, each of the block bodies 2, 2 is substantiallyidentical to each other in the shape. Therefore, hereinafter, thedescription will be made on one of the pair of elongated block bodies 2,2 as a representative.

As shown in FIG. 1, the block body 2 is constituted from a polyhedralbody which is formed from a plurality of surfaces having a first surface31, a second surface 32, a third surface 33, a fourth surface 34, afifth surface 35 and a sixth surface 36.

As shown in FIG. 3, the first surface 31 constitutes a contact surfaceto be made contact with the vertebral body 101 and the second surface 32constitutes a contact surface making contact with the vertebral body 102in a state of inserting the block body 2 into the intervertebral space(inserted state). Further, in the inserted state, the third surface 33defines an inside space 103 in the intervertebral space and the fourthsurface 34 defines an outside space 103 in the intervertebral space.

In the present embodiment, the third surface 33 constitutes a curvedconcave surface and the fourth surface constitutes a curved convexsurface. This makes it possible to easily insert the block body 2 intothe intervertebral space so as to correspond to shapes of the vertebralbodies (vertebral bone).

Further, the first surface 31, the second surface 32, the fifth surface35 and the sixth surface 36 constitute substantially a plane surface(flat surface), respectively. Among of them, in particular, the planesurfaces (flat surfaces) of the first surface 31 and the second surface32 make it possible to reliably be in the block body 2 contact with thevertebral bodies 101, 102.

Further, the first surface 31 and the second surface 32 havesubstantially an equal length. The third surface 33 and the fourthsurface 34 also have substantially an equal length. The fifth surface 35and the sixth surface 36 also have substantially an equal length.

In other words, the block body 2 is formed so that a cuboid is curvedalong a longitudinal direction thereof so as to concave the thirdsurface 33 and convex the fourth surface 34.

In this regard, the vicinities of corner portions formed by makingcontact with each surface are chamfered, respectively. This makes itpossible to prevent breakages such as a crack of the block body 2. Inaddition to that, it is possible to easily insert the block body 2 intothe intervertebral space with making no contact with the vertebralbodies 101 and 102.

Dimension such as the length of such a block body 2 in a front-backdirection (L₁ in FIG. 1), the length thereof in a horizontal direction(L₂ in FIG. 1) and the length thereof in an upper-lower direction (L₃ inFIG. 1) is arbitrarily dependent from a kind of vertebral body such ascervical vertebra and lumbar vertebra or cases. The dimension, however,is set to fall within ranges as follows.

The length of such a block body 2 in the front-back direction (L₁ inFIG. 1) is preferably set to the range of about 6 to 25 mm and morepreferably the range of about 8 to 22 mm.

The length of the block body 2 in the horizontal direction (L₂ inFIG. 1) is preferably set to the range of about 4 to 25 mm, morepreferably the range of about 10 to 25 mm and even more preferably therange of about 16 to 21 mm.

The length of the block body 2 in the upper-lower direction (L₃ inFIG. 1) is preferably set to the range of about 6 to 15 mm and morepreferably the range of about 9 to 12 mm.

Meanwhile, the block body 2 of the present invention includes aframe-shaped dense part 25 and a porous part 21 provided inside thedense part 25. A porosity of at least a surface of the porous part 21 islarger than a porosity of the dense part 25. In other words, the blockbody 2 has the porous part 21 and the dense part 25 provided at an outercircumference side of the porous part 21. The configuration makes itpossible to maintain a shape of the block body 2 due to the existence ofthe dense part 25 even if stress is applied to the block body 2 in theinserted state. Therefore, it is possible to reliably prevent orsuppress the porous part 21 from being broken while maintaining anappropriate size of the intervertebral space. Further, it is ensured toachieve the bone fusion between the vertebral bodies 101, 102 and theporous part 21 promptly.

In the present embodiment, the dense part 25 has a lower frame portion(first frame portion) 251 and an upper frame portion (second frameportion) 252 which have a shape corresponding to the shape of the blockbody 2 in the plane view as shown in FIG. 1(a). The dense part 25 alsohas a plurality of connecting portions 253 which connect the lower frameportion 251 and the upper frame portion 252.

The configuration forms the dense part 25 defining the whole shape ofthe block body 2. In other words, the block part 2 has the porous part21 having a plurality of corner portions and the dense part 25 formedalong (so as to surround) the corner portions of the porous part 21. Inthe inserted state, the lower frame portion 251 is in contact with thevertebral body (one of the vertebral bodies) 102 and the upper frameportion 252 is in contact with the vertebral body (the other of thevertebral bodies) 101.

In the present embodiment, the plurality of connecting portions 253includes four connecting portions provided at corner portions of each ofthe frame portion 251 and the frame portion 252, and two connectingportions provided at central portions of the frame portion 251 and theframe portion 252, respectively. Such connecting portions 253 have afunction of supporting the lower frame portion 251 and the upper frameportion 252 as a supporting post. Therefore, in the inserted state, whenstress is applied to the block body 2, it is possible to reliablyprevent or suppress the lower frame portion 251 and the upper frameportion 252 from approaching to each other. In this regard, the porosityof the dense part 25 is not limited particularly, as long as theporosity is lower than that of the porous part 21. Specifically, theporosity of the dense part 25 is preferably in the range of about 3 to50%, more preferably in the range of about 10 to 40% and even morepreferably in the range of about 15 to 35%. It is noted that theporosity of the dense part 25 may be substantially 0%.

As described above, the connecting portions 253 exhibit the function asthe supporting post and support the lower frame portion 251 and theupper frame portion 252. In this specification, such a structure isreferred to as “supporting post structure”.

The porous part 21 is configured to be filled into the frame-shapeddense part 25 and exposed to the surfaces 31 to 36 of the block body 2from the inside of the dense part 25.

The porosity of at least the surface of the porous part 21 may be largerthan the porosity of the dense part 25. Therefore, the porous part 21may have a dense portion at the inside thereof. However, it is preferredthe whole of the porous part 21 is constituted from a porous body. Thisconstitution ensures to achieve the bone fusion between the vertebralbodies 101, 102 and the porous part 21 promptly. Therefore, the blockbody 2 is fused into the intervertebral space reliably.

The porosity of the porous part 21 is not limited particularly as longas the porosity of the porous part 21 is larger than the porosity of thedense part 25. Specifically, the porosity of the porous part 21 is inthe range of about 20 to 95%, more preferably in the range of about 50to 85% and even more preferably in the range of about 55 to 85%. Thismakes it possible to achieve the bone fusion between the vertebralbodies 101, 102 and the porous part 21 promptly. In the case where theporosity of the porous part 21 falls within such ranges, it is possibleto reliably prevent or suppress the block body 2 from being broken whenthe stress is applied to the block body 2 in the inserted state. This isbecause the block body 2 has the dense part 25 in addition to the porouspart 21. In this regard, it is to be noted that it becomes easy to formcommunicating holes, in which holes are connected with each other, inthe porous part 21 if the porosity of the porous part 21 is equal to orlarger than 55%.

Further, it is preferred that an osteoinductive factor is carried oninner surfaces of the communicating holes (holes) of the porous part 21.This makes it possible to achieve the bone fusion between the vertebralbodies 101, 102 and the porous part 21 promptly.

The osteoinductive factor is not limited particularly as long as it hasan activity of promoting bone formation by deriving differentiatedosteoblast from an undifferentiated mesenchymal cell. Specifically, bonemorphogenic protein (BMP) is used preferably as the osteoinductivefactor.

Examples of BMP include BMP-1, BMP-2, BMP-3, BMP-4, BMP-5, BMP-6, BMP-7,BMP-8, BMP-9, BMP-12 (these are a homodimer), a heterodimer of theirBMPs or a modified body thereof, and the like.

In the present invention, the block body 2 can be produced by using aproducing method as described later. According to such a producingmethod, it is possible to form the dense part 25 and the porous part 21integrally. Such a block body 2 is capable of reliably preventing stressfrom unevenly being applied to the dense part 25 or the porous part 21when the stress is applied in the inserted state. In this case, each ofthe surfaces 31, 32, 33, 34 constitutes the flat surface, namely asurface having no gap between the dense part 25 and the porous part 21.Therefore, it is possible to particularly make the porous part 21contact with the vertebral bodies 101, 102 in the first surface 31 andthe second surface 32. Consequently, it is possible to achieve the bonefusion between the vertebral bodies 101, 102 and the porous part 21promptly.

In the present invention, a titanium based material such as titanium ora titanium alloy is mainly used as a constituent material of such ablock body 2, namely constituent materials of the dense part 25 and theporous part 21.

The titanium based material has high biocompatibility and excellentstrength, and therefore is used as the constituent material of the blockbody 2 reliably. In the titanium based material, the titanium alloy ispreferably used as the constituent material of the dense part 25requiring the excellent strength in a constituent member of the blockbody 2. This is because the titanium alloy has more excellent strength.Further, examples of the titanium alloy are not limited particularly,but include an alloy in which one or more of Al, Sn, Cr, Zr, Mo, Ni, Pd,Ta, Nb, V, Pt and the like are added to Ti of a main component, and thelike. Examples of such an alloy include Ti-6A1-4V, Ti-29Nb-13Ta-4.6Zrand the like.

The pair of block bodies 2 as described above is inserted between thevertebral body 101 and the vertebral body 102 (intervertebral space)side by side with each other.

By inserting the block body 2 into the intervertebral space, a space 103is formed in an area of the intervertebral space in which no block body2 exists. A grafted bone (particular, autologous bone) as a filler isfilled into the space 103, so that it is ensured to achieve the bonefusion between the vertebral body 101 and the vertebral body 102 throughthe block body 2 and the grafted bone more reliably and promptly.

Further, the spacer 1 is constituted from the pair of block bodies 2, 2.Therefore, if the arrangement of the block bodies 2, 2 is changed, thatis, they are arranged in a state of spacing the front ends or the backends of the block bodies 2 from each other and/or approaching them toeach other, it becomes possible to treat an appropriate cure dependingupon cases.

The spacer 1 as described above, for example, can be produced asfollows.

<1> First, prepared is a frame-shaped dense body to become the densepart 25 by performing a debinding process and sintering process.

Such a frame-shaped dense body can be obtained easily by preparing asheet-shaped dense body constituted of the titanium based material andcutting the sheet-shaped dense body in a predetermined shape and size byusing a slice cut method such as a laser cut method, a water jet method,a discharge wire method and an ultrasound ablation method.Alternatively, the frame-shaped dense body is prepared by using a slurryof which concentration is adjusted so that the porosity thereof is moresmaller, which is the same process as that of a green body to become theporous part 21 as described later. Moreover, the frame-shaped dense bodyis also prepared by using a slurry of which composition and an additiveamount of a foaming agent (0% to) are adjusted, which is the sameprocess as that of the green body to become the porous part 21 asdescribed later.

<2> Next, prepared is a green body to become the porous part 21 byperforming a debinding process and a sintering process.

<2-1> First, prepared is a slurry containing metal powder and a foamagent. Powder constituted of the titanium based material described aboveor an oxidant thereof is used as the metal powder.

Further, an average particle size of particles of the metal powder isnot limited particularly, but preferably in the range of about 0.5 to 50μm and more preferably in the range of about 3 to 30 μm. By using themetal powder including the particles having such a size, it becomespossible to set the porosity of the obtained porous part 21 and anaverage pore size of pores thereof to a predetermined value. In thisregard, it is to be noted that the average particle size of theparticles of the metal powder can be obtained by a laser diffractometryand the like.

An amount of the metal powder in the slurry is preferably in the rangeof about 30 to 80 mass % and more preferably in the range of about 40 to70 mass %. By setting the amount of the metal powder to such ranges, itbecomes possible to reliably set the porosity of the obtained porouspart 21 and the average pore size of the pores thereof to thepredetermined value.

Examples of the foam agent is not limited particularly, but include asurfactant, a volatile organic solvent and the like. A water-insolublehydrocarbon-based organic solvent having a carbon number of 5 to 8 ispreferably used as the volatile organic solvent. Further, neopentane,hexane, heptanes and cyclohexane are more preferably used. The use ofsuch a foam agent makes it possible to obtain the porous part 21 havinga high porosity with ease.

Such a slurry contains a water-soluble resin binder and water. Inaddition to that, the slurry contains other components such as aplasticizer, an organic solvent and the like, if needed.

Examples of the water-soluble resin binder include methylcellulose,hydroxyl propyl methylcellulose, polyvinyl butyral, polyvinyl alcoholand the like. These materials may be used singly or in combination oftwo or more of them. A skeleton of the porous part 21 is formed well byusing the slurry containing the water-soluble resin binder.

Examples of the plasticizer include glycerin, ethylene glycol,polyethylene glycol, and the like.

Examples of the organic solvent include methanol, ethanol, isopropanol,and the like.

<2-2> Next, the prepared slurry is applied onto a base in a sheet shape,then the applied slurry is heated and foamed and thereafter is dried toobtain a green body (green sheet).

A method of molding the slurry in the sheet shape is not limitedparticularly, but is preferably a doctor blade method.

The heating process is not limited particularly, but is preferablyperformed under a high humidity atmosphere having humidity of 80% ormore. By controlling a temperature condition at this time, it ispossible to uniformly control pore sizes of a huge number of foam poresformed by acts of the foam agent in the whole of the slurry. As aresult, it is possible to form a three dimensional skeleton constitutedof the slurry containing the metal powder.

At this time, the foam pores are formed in a flat shape on a contactsurface (back surface) between the slurry and the base. On the otherhand, on a surface (front surface) of the slurry opposite to the base,foam pores inflated three-dimensionally due to free foam are formed.Therefore, according to the producing method as the present embodiment,a green body having an asymmetric foam structure on the back surface andthe front surface each other is formed.

Further, the drying process of the slurry in which the foam pores havebeen formed is performed by heating at a temperature of 100° C. or lessunder the atmosphere or an inert gas atmosphere. This makes it possibleto reliably remove moisture contained in the slurry while maintainingthe foam pores included in the slurry.

<2-3> Next, the obtained green body is peeled off from the base.Thereafter, the green body is cut in a predetermined shape and size byusing the slice cut method described above. The cut green body to becomethe porous part 21 by performing the debinding process and sinteringprocess is obtained.

<3> Next, the cut green body (porous part 21 before performing thedebinding process and sintering process) is placed into the flame-shapeddense body (dense part 25 before performing the debinding process andsintering process), and thereafter they are heated in this state. Byperforming the debinding process and sintering process of the cut greenbody and the flame-shaped dense body, a block body 2 is obtained as theporous part 21 and the dense part 25. In this regard, it is to be notedthat the porosity of the dense part 25 after performing the debindingprocess and sintering process is preferably in the range of 3 to 50%.

The cut green body and the flame-shaped dense body are debinded at atemperature within the range of about 350 to 600° C. for about 1 to 10hours. The debinding under such conditions makes it possible todecompose and remove components other than the metal powder included inthe cut green body and the flame-shaped dense body while maintaining afoam pore structure. Consequently, it is possible to change the cutgreen body and the flame-shaped dense body to a metal brown body havinga skeleton structure in which the metal powder is aggregated.

Further, the cut green body and the flame-shaped dense body (metal brownbody) after performing the debinding process are sintered at atemperature within the range of about 1100 to 1350° C. for about 1 to 10hours under a non-oxidizing atmosphere. The sintering process under suchconditions makes it possible to sinter the metal powder whilemaintaining the foam pore structure. In addition to that, it is possibleto diffuse the metal powder in the cut green body and the flame-shapeddense body after performing the debinding process. As a result, thedense part 25 and the porous part 21 are diffusion-bonded together.Further, it is possible to sinter the metal powder while maintaining thefoam pore structure, so that it is possible to obtain the block body 2in which the dense part 25 and the porous part 21 are bonded togetherfirmly.

In this regard, a degree of vacuum in the non-oxidizing atmosphere ispreferably 5.0×10⁻² Pa or less. The non-oxidizing atmosphere ispreferably an argon atmosphere.

As described above, by performing the debindng process and the sinteringprocess, the cut green body and the flame-shaped dense body change tothe porous part 21 and the dense part 25, respectively, thereby enablinga block body 2 in which the porous part 21 and the dense part 25 arebonded (integrated) together firmly to obtain.

In the case where the flame-shaped dense body is constituted of thetitanium based alloy (material), frame-shaped dense bodies are formedseparately in advance, and then the separately formed frame-shaped densebodies and the porous part 21 (sintered cut green body) are assembled.Next, end portions of the separately formed frame-shaped dense bodiesare welded to each other by laser and the like to obtain an assembledbody. Thereafter, the assembled body is subjected to a heating treatmentat a temperature in the range of 800 to 1050° C. for 1 to 10 hours underthe non-oxidizing atmosphere (argon atmosphere or vacuum). This makes itpossible to change the frame-shaped dense bodies to the dense part 25and obtain a block body 2 by diffusion-bonding between the dense part 25and the porous part 21. In this regard, when the separately formedframe-shaped dense bodies and the porous part 21 are assembled, theporous part 21 included in the assembled body formed so that eachsurface becomes a flat surface is used. That is, the porous part 21 inwhich grooves capable of containing the frame-shaped dense bodies areformed is used.

Second Embodiment

Next, description will be made on a second embodiment of a vertebralbody space according to the present invention.

FIG. 4 is a plan view (a), a front view (b) and a side view (c) whichshow the second embodiment of a block body constituting the vertebralbody spacer of the present invention.

In the following description, the description will be made on a blockbody 2 shown in FIG. 4. The description will be made by focusing ondifferent points from the block body 2 shown in FIG. 1 to FIG. 3 and thedescription on the common points is omitted.

The block body 2 shown in FIG. 4 is the same as the block body 2 shownin FIG. 1 to FIG. 3 except that a shape of the whole thereof isdifferent.

In the present embodiment, both a first surface and a second surface 32constitute a curved convex surface. The first surface 31 and the secondsurface 32 are connected to each other at an end portion on a frontside. Thus, a sixth surface 36 is omitted. Further, each of a thirdsurface 33, a fourth surface 34 and a fifth surface 35 constitutessubstantially a flat surface. As described above, since both the firstsurface 31 and the second surface 32 of the block body 2 constitute thecurved convex surface, it is possible to insert the block body 2 intothe intervertebral space so as to slide that along the curved convexsurface. For this reason, it is possible to perform an insertingoperation into the intervertebral space more easily whit making theblock body 2 no contact with the vertebral bodies 101 and 102.

Further, in the present embodiment, a hole portion 255 is provided at asubstantial center of a dense part which forms a bonding part betweenthe first surface 31 and the second surface 32. In the case where theblock body 2 is inserted into the intervertebral space by using a jig,this hole portion 255 is used to fix the block body 2 to the jig byinserting a convex portion of the jig thereinto. This makes it possibleto insert the block body 2 into the intervertebral space with ease byusing the jig.

The block body 2 having such a whole shape has a lower frame portion 251and an upper frame portion 252 which have a shape corresponding to theshape of the block body 2 in the plane view as shown in FIG. 4(a). Theblock body 2 also has a connecting portion 253 which connects the lowerframe portion 251 and the upper frame portion 252. In the presentembodiment, the connecting portion 253 is constituted from one wideconnecting portion provided at an end portion on a back side of theframe portion 251 and the frame portion 252. Further, each of the frameportion 251 and the frame portion 252 is curved and directly connectedat the end portion on the front side to each other. Thus, a connectingportion is omitted at the end portion on the front side of the frameportion 251 and the frame portion 252.

The block body 2 of the present embodiment configured as described abovecan be also used as the block body 2 of the first embodiment and obtainthe same effects as those of the block body 2 (spacer 1) of the firstembodiment.

Third Embodiment

Next, description will be made on a third embodiment of a vertebral bodyspace according to the present invention.

FIG. 5 is a plan view (a), a front view (b) and a side view (c) whichshow the third embodiment of a block body constituting the vertebralbody spacer of the present invention.

In the following description, the description will be made on a blockbody 2 shown in FIG. 5. The description will be made by focusing ondifferent points from the block body 2 shown in FIG. 1 to FIG. 3 and thedescription on the common points is omitted.

The block body 2 shown in FIG. 5 is the same as the block body 2 shownin FIG. 1 to FIG. 3 except that a configuration of the dense part 25 isdifferent.

In the present embodiment, as shown FIG. 5, each of connecting portions253 is placed diagonally in an upper-lower direction of the block body2. The adjacent connecting portions 253 make contact with (connect to)each other at an end portion thereof (a portion connecting a lower frameportion 251 and an upper frame portion 252). In other words, a densepart 25 constituted from the lower frame portion 251, the upper frameportion 252 and the connecting portions 253 makes a truss structure.This ensures that the connecting portions 253 exhibit a functionreliably of supporting the lower frame portion 251 and the upper frameportion 252 as a supporting post, thereby improving strength of thedense part 25. Therefore, it is possible to reliably suppress or preventthe dense part 25 from being broken when stress is applied to the blockbody 2 in the inserted state.

The block body 2 of the present embodiment configured as described abovecan be also used as the block body 2 of the first embodiment and obtainthe same effects as those of the block body 2 (spacer 1) of the firstembodiment.

Fourth Embodiment

Next, description will be made on a fourth embodiment of a vertebralbody space according to the present invention.

FIG. 6 is a plan view (a), a front view (b) and a side view (c) whichshow the fourth embodiment of a block body constituting the vertebralbody spacer of the present invention.

In the following description, the description will be made on a blockbody 2 shown in FIG. 6. The description will be made by focusing ondifferent points from the block body 2 shown in FIG. 1 to FIG. 3 and thedescription on the common points is omitted.

The block body 2 shown in FIG. 6 is the same as the block body 2 shownin FIG. 1 to FIG. 3 except that a plurality of conical projectionportions 41 is provided so as to project from a first surface 31 and asecond surface 32.

In the present embodiment, needle bodies 40 having projection portions41 at both ends thereof are inserted into a plurality of through holesprovided to pass through a porous part 21 so that the projection parts41 are projected from the porous part 21. As described above, theplurality of projection portions 41 projecting from the first surface 31and the second surface 32 is provided with the block body 2. Therefore,the projection portions 41 is spiked (anchored) on the lower surface ofthe vertebral body 101 and the upper surface of the vertebral body 102when the block body 2 is inserted into the intervertebral space. Bydoing so, it is possible to make the first surface 31 and the secondsurface 32 firm contact with the vertebral body 101 and the vertebralbody 102, respectively. Consequently, it is possible to reliably preventthe block body 2 from dropping off from the intervertebral space.

It is preferred that the needle bodies 40 configured as described aboveare constituted from a dense part like the dense part 25. The needlebodies 40 exhibit more excellent strength, so that it is possible toreliably prevent or suppress the needle bodies 40 from being broken whenstress is applied to the block body 2 in the inserted state.

The block body 2 of the present embodiment configured as described abovecan be also used as the block body 2 of the first embodiment and obtainthe same effects as those of the block body 2 (spacer 1) of the firstembodiment.

In this case, it is to be noted that a shape of each of the projectionportions 41 is not limited to the conical shape as shown in FIG. 6, forexample, it may be a pyramid shape such as a quadrangular pyramid shapeor a triangular pyramid shape.

Fifth Embodiment

Next, description will be made on a fifth embodiment of a vertebral bodyspace according to the present invention.

FIG. 7 is a plan view (a), a front view (b) and a side view (c) whichshow a fifth embodiment of a block body constituting a vertebral bodyspacer of the present invention.

In the following description, the description will be made on a blockbody 2 shown in FIGS. 7 and 8. The description will be made by focusingon different points from the block body 2 shown in FIG. 1 to FIG. 3 andthe description on the common points is omitted.

The block body 2 shown in FIG. 7 is the same as the block body 2 shownin FIG. 1 to FIG. 3 except that a connecting portion 50 of rotatablyconnecting a pair of block bodies 2 to each other is provided with thepair of block bodies 2.

In the present embodiment, the connecting portion 50 has a plate-shapedconnection finger 51 provided at an end portion on a front side of athird surface 33 of one of the block bodies 2 and a plate-shapedconnection finger 52 provided at an end portion on a front side of athird surface 33 of the other of the block bodies 2. A road-shaped body53 is formed at an end portion on a side of the connection finger 51opposite to the block body 2 so as to project toward an upper direction.A through hole 54 is formed at an end portion on a side of theconnection finger 52 opposite to the block body 2. The two block bodies2 are connected to each other through the connecting portion 50 byinserting the rod-shaped body 53 into the through hole 54. Further, ahinge portion is formed by inserting the rod-shaped body 53 into thethrough hole 54, so that it is possible for the block bodies to approachto and space from each other at the hinge portion as a center ofrotation. In other words, the block bodies 2 are capable of rotating ina horizontal direction with respect to a first surface 31.

According to the spacer 1 having such an configuration, it is possibleto change a position of each block body 2, namely to perform operationseasily and rapidly of spacing front ends and back ends of block bodies 2from each other and/or approaching them to each other, which depend oncases. Therefore, it becomes possible to perform an appropriate cure byusing such a spacer 1 promptly. Further, since the block bodies 2 areconnected to each other through the connecting portion 50, it is easy toaccurately position them in the intervertebral space in the insertedstate.

The block body 2 of the present embodiment configured as described abovecan be also used as the block body 2 of the first embodiment and obtainthe same effects as those of the block body 2 (spacer 1) of the firstembodiment.

The description has been made on the embodiments of the vertebral bodyspace according to the present invention as shown in the drawings.However, the present invention is not limited to them.

For example, any configuration of the first to fifth embodiments may becombined arbitrarily in the vertebral body space according to thepresent invention.

Further, in each of the embodiments, the porous part 21 is constitutedfrom one member, however, may be constituted by laminating (attaching) aplurality of sheet-shaped bodies each having a different porosity. Inthis case, it is possible to give anisotropy to the strength of theporous part 21, thereby improving flexibility in a design of the blockbody 2 (spacer 1).

Further, in each of the embodiments, the description has been made onthe case of inserting the pair of block bodies 2 into the intervertebralspace. However, the case is not limited thereto, and may be a case ofinserting one block body 2 into the intervertebral space. In this case,the block body 2 is inserted in the front side of the intervertebralspace so that the fourth surface 34 faces to the front side and thethird surface 33 faces to the back side.

Moreover, the filler is not limited to the grafted bone (autologousbone), for example, may be powder or granule of a calcium phosphatebased compound, a calcium phosphate based cement and the like.

INDUSTRIAL APPLICABILITY

The vertebral body spacer of the present invention is capable ofmaintaining an appropriate size between vertebral bodies (intervertebralspace). Further, the vertebral body spacer of the present invention iscapable of reliably preventing the vertebral body spacer from beingbroken irrespecitve of cases and a position of the intervertebral space,and thereby capable of achieving bone fusion between the vertebral bodyspacer and the vertebral bodies promptly. Moreover, a space of fillingthe filler into the intervertebral space is ensured by inserting thevertebral body spacer thereinto. For these reasons, by filling thegrafted bone to such a space, it is possible to reliably and promptlyachieve the bone fusion between the vertebral bodies through thevertebral body spacer and the grafted bone. Accordingly, the presentinvention has industrial applicability.

What is claimed is:
 1. A vertebral body spacer to be used by beinginserted between vertebral bodies, comprising; at least one block bodyconstituted of titanium or a titanium alloy as a main component thereof,and the block body having a pair of contact surfaces to be made contactwith the vertebral bodies, and wherein the block body includes aframe-shaped dense part having a porosity of 10 to 40% and a porous partprovided inside the dense part, and a porosity of at least a surface ofthe porous part is larger than a porosity of the dense part, wherein thedense part includes a first frame portion configured to contact one ofthe vertebral bodies and a second frame portion configured to contactthe other of the vertebral bodies, wherein one of surface of the pair ofcontact surfaces is constituted from the first frame portion of thedense part and the porous part, and the other of surface of the pair ofcontact surfaces is constituted from the second frame portion of thedense part and the porous part, and wherein each surface of the pair ofcontact surfaces constitutes a curved convex surface.
 2. The vertebralbody spacer as claimed in claim 1, wherein the dense part and the porouspart are integrally formed.
 3. The vertebral body spacer as claimed inclaim 1, wherein the porous part has a plurality of corner portions, andthe dense part is provided along the plurality of corner portions of theporous part.
 4. The vertebral body spacer as claimed in claim 1, whereinthe block body is constituted from a polyhedral body defined by aplurality of surfaces including the pair of contact surfaces, and eachof the plurality of surfaces constitutes a flat surface.
 5. Thevertebral body spacer as claimed in claim 1, wherein at least one blockbody is constituted from a pair of block bodies.
 6. The vertebral bodyspacer as claimed in claim 1, wherein a whole of the porous part isconstituted from a porous body.
 7. The vertebral body spacer as claimedin claim 1, wherein an osteoinductive factor is carried on the porouspart.
 8. The vertebral body spacer as claimed in claim 1, wherein thedense part includes at least one connecting portion connecting the firstframe portion and the second frame portion to each other, and whereinthe connecting portion serves as a supporting post.
 9. The vertebralbody spacer as claimed in claim 1, wherein the block body is constitutedfrom a polyhedral body defined by a plurality of surfaces having thepair of contact surfaces, a first surface connecting the pair of contactsurfaces at a front end of the block body and a second surfaceconnecting the pair of contact surfaces at a back end of the block body,and wherein the pair of contact surfaces are connected to each other atan end portion on the front end of the block body, so that the firstsurface is omitted.